Weird problem with Mongo ObjectId

I have a meteor app with angularJs.
When it starts, it works just fine, but after I start using it (inserting and removing documents), I keep getting this error in the console (with different items):

Exception in queued task: Error: Item a2e73bad917429a782169256 already present in OrderedDict
    at OrderedDict.putBefore (http://localhost:3000/packages/ordered-dict.js?hash=bacdd1852075630a01f7de783e5e8e8aa8541cdc:105:13)
    at Object.addedBefore (http://localhost:3000/packages/minimongo.js?hash=66cc6ab213289f154f49d61566dba8ff9dfc33b2:3683:19)
    at http://localhost:3000/packages/minimongo.js?hash=66cc6ab213289f154f49d61566dba8ff9dfc33b2:410:13
    at Meteor._SynchronousQueue.runTask (http://localhost:3000/packages/meteor.js?hash=e3f53db3be730057fed1a5f709ecd5fc7cae1229:721:11)
    at Meteor._SynchronousQueue.flush (http://localhost:3000/packages/meteor.js?hash=e3f53db3be730057fed1a5f709ecd5fc7cae1229:749:10)
    at Meteor._SynchronousQueue.drain (http://localhost:3000/packages/meteor.js?hash=e3f53db3be730057fed1a5f709ecd5fc7cae1229:757:12)
    at LocalCollection.Cursor.observeChanges (http://localhost:3000/packages/minimongo.js?hash=66cc6ab213289f154f49d61566dba8ff9dfc33b2:458:35)
    at Function.LocalCollection._observeFromObserveChanges (http://localhost:3000/packages/minimongo.js?hash=66cc6ab213289f154f49d61566dba8ff9dfc33b2:3820:23)
    at LocalCollection.Cursor.observe (http://localhost:3000/packages/minimongo.js?hash=66cc6ab213289f154f49d61566dba8ff9dfc33b2:343:28)
    at Scope.$$Reactive.$$handleCursor (http://localhost:3000/packages/modules.js?hash=43d3c78e1c7a8ba93b2861fa558728d6bfa98fb3:3127:31)

I checked the collection before and after using the app, and I found this problem (when I ran
myCollection.find().collection._docs._map:

For a reason I can’t find, the ObjectID of these documents change to take other documents’ objectID.
Anyone has any explanation why this happens?

PS: the inserts and removes I ran don’t occur on the affected collection, they just use the Ids from there